Molecular mechanisms of motor neuron development

描述（由申请人提供）：本提案的主要目标是了解运动神经元分化和特化的分子机制。类维生素A（RA）信号对于在脊髓运动神经元分化期间同步神经源性和运动神经元特化途径是必需的，并且这些事件由RA应答基因GDE 2介导。GDE 2编码具有细胞外甘油磷酸二酯磷酸二酯酶（GDPD）结构域的六跨膜蛋白。GDPD活性是GDE 2协调细胞周期退出和运动神经元特化的能力所必需的，揭示了GDPD代谢和运动神经元分化之间的新联系。GDPD结构域位于细胞外的GDE 2的独特拓扑结构和缺乏功能先例强烈预测了参与运动神经元分化的新分子网络的发现。为了鉴定这样的网络，使用无偏筛选来分离与GDE 2相互作用的蛋白质。两个不同的信号通路的组件进行了鉴定。在这项提议中，体外结构-功能分析将与体内功能丧失和获得研究相结合，以研究这些信号通路如何与GDE 2整合以促进运动神经元分化。虽然GDE 2表达的起始发生在分化细胞中，但GDE 2表达维持在终末分化的运动神经元中;这表明GDE 2可能对以后的运动神经元功能或存活具有关键的额外作用。为了确定GDE 2在运动神经元发育的不同阶段的功能，将使用小鼠遗传学来消除分化和有丝分裂后运动神经元中的GDE 2。将分析所得胚胎在运动神经元分化、运动神经元特化、运动轴突靶识别和运动神经元存活方面的缺陷。这些实验将确定两种不同的信号通路如何与GDPD依赖的神经元分化模式协同作用，并进一步推进目前对细胞分化中涉及的调控网络的理解。此外，这些研究还将探讨GDE 2在对神经元功能和存活至关重要的各种细胞过程中的潜在作用。

DESCRIPTION (provided by applicant): The major goals of this proposal are to understand the molecular mechanisms of motor neuron differentiation and specification. Retinoid (RA) signals are necessary for synchronizing neurogenic and motor neuron specification pathways during spinal motor neuron differentiation and these events are mediated by the RA-responsive gene, GDE2. GDE2 encodes a six transmembrane protein with an extracellular glycerophosphodiester phosphodiesterase (GDPD) domain. GDPD activity is required for GDE2's ability to coordinate cell-cycle exit and motor neuron specification, revealing a novel link between GDPD metabolism and motor neuron differentiation. The distinctive topology of GDE2 where the GDPD domain is extracellular and the lack of functional precedent strongly predicts the discovery of new molecular networks involved in motor neuron differentiation. To identify such networks, unbiased screens were used to isolate proteins that interact with GDE2. Components of two different signaling pathways were identified. In this proposal, in vitro structure-function analyses will be combined with in vivo loss- and gain- of function studies to investigate how these signaling pathways integrate with GDE2 to promote motor neuron differentiation. While onset of GDE2 expression occurs in differentiating cells, GDE2 expression is maintained in terminally differentiated motor neurons; suggesting that GDE2 may have additional roles critical for later motor neuron function or survival. To define the function of GDE2 at different stages of motor neuron development, mouse genetics will be used to ablate GDE2 in differentiating and postmitotic motor neurons. Resultant embryos will be analyzed for defects in motor neuron differentiation, motor neuron specification, motor axon target recognition and motor neuron survival. These experiments will determine how two different signaling pathways synergize with GDPD- dependent modes of neuronal differentiation and further advance current understanding of the regulatory networks involved in cell differentiation. In addition, these studies will investigate potential roles for GDE2 in diverse cellular processes critical for neuronal function and survival.